method for retrieving list of listeners of given type

frontend-js/src/main/js/ObjectWithListeners.js

@@ -159,6 +159,13 @@ ObjectWithListeners.prototype.callListeners = function(type, arg) {
   return Promise.all(promises);
 };
 
+ObjectWithListeners.prototype.getListeners = function(type) {
+  if (this._validListeners[type] === undefined) {
+    throw new Error("Unknown listener type: " + type);
+  }
+  return this._validListeners[type];
+};
+
 /**
  * Fires property change listeners for a given property name.
  *